NORMAL PROCESSES OF ENERGY METABOLISM 609 



Referred to body weight the metabolism even in men of nearly the 

 same size and weight may differ considerably. The results obtained by 

 Jaquet and by Caspari vary from 0.8 Cal. per kgm. and hour to 1.6 Cal. per 

 kgm. and hour. The latter figure was obtained by Caspari upon a trained 

 athlete. Benedict and Smith have also shown that athletes have in general 

 a higher basal metabolism than untrained individuals of the same physical 

 measurements. Fat persons generally have, as would be expected, a lower 

 metabolism per unit of weight than lean ones ; for the fat tissues are rela- 

 tively inactive. Other differences on the basis of weight may be accounted 

 for, to some extent at least, by differences in muscular tonus, and differ- 

 ences in "endocrine efficiency." 



As a convenient reference point the average obtained by Tigerstedt 

 from a long series of determinations of the basal metabolism in man 

 (namely, 1.04 calories per kgm. and hour) should be borne in mind. The 

 average individual variation from this average is roughly plus or minus 

 10 per cent. 



The physical characteristic which has proved to be most useful as a 

 criterion or measure of metabolism is the surface area of the body. Rub- 

 ner's original study on full-grown dogs is given in Table 19. Here it 



. TABLE 19 

 INFLUENCE OF BODY SIZE ON METABOLISM (Rubner) 



was demonstrated how much more nearly proportional to surface the 

 metabolism is than to body weight. While it is true that absolutely basal 

 conditions were not present the animals were not observed to move about 

 to any considerable extent. The original observations of Richet upon rab- 

 bits likewise are worthy of repetition here. The heat given off by radia- 

 tion from the animal's body caused the air enclosed within the walls of the 

 calorimeter to expand and to displace water in the siphon (page 582). 

 Heat is expressed in Table 20 as the number of c.c. of water displaced. 

 The number expressing the surface of the animal was found by Richet by 

 regarding the body as a geometric sphere. Since its weight (volume) 



is equal to and the surface by 4 it R 2 , the volume would be to the 



2 



surface as 4.2R 3 : 12. 6R 2 . Finding R from the known weight (volume) 

 the relative surface was obtained by multiplying the square of this number 



